# X(3872) in a hot pion bath

## TL;DR

This paper investigates how a hot pion environment affects the properties of the exotic $X(3872)$ meson, suggesting it becomes broader and shifts above the $D D^*$ threshold at high temperatures, impacting its detection in heavy-ion collisions.

## Contribution

The study provides the first finite temperature analysis of the $X(3872)$ as a $Dar D^*+c.c.$ molecule, revealing significant width broadening and mass shifts in hot pionic environments.

## Key findings

- $X(3872)$ develops a width of tens of MeV at 100-150 MeV temperatures.
- The mass of $X(3872)$ shifts above the $D D^*$ threshold in hot environments.
- Implications for $X(3872)$ detection in relativistic heavy-ion collisions.

## Abstract

Right since its discovery in 2003 by the Belle collaboration, establishing the nature of the $X(3872)$ meson has been one of the main priorities in the field of quarkonium physics. Not qualifying as a conventional $c\bar{c}$ state, the multiquark structure of this exotic meson has received very different interpretations, ranging from a compact tetraquark configuration to an extended $D\bar D^*+c.c.$ molecule. In this work we explore the effect that a hot pion bath may have in the properties of the $X(3872)$, assuming this state to be a $D\bar D^*+c.c.$ molecule. We derive the finite temperature effects on the $X(3872)$ from a coupled channels unitarized amplitude, obtained including the properties of the charmed mesons under such conditions. We find that the $X(3872)$ develops a subtantial width, of the order of a few tens of MeV, in hot pionic environments at temperatures $100-150$ MeV, and its nominal mass moves above the $D D^*$ threshold. The fact that the $X(3872)$ in a hot pion gas may no longer be a narrow resonance needs to be considered in the estimation of production yields in relativistic heavy-ion collisions.